Data Sheet

dScript

dScript User Manual v2.15

Non-volatile variables

Some modules have an EEPROM for storing a small number of variables when power is

switched off. The dS1242 & dS3484 have a 512 byte EEPROM on board.

Either string or var variables can be located in this non-volatile memory. To declare a non-

volatile var use eevar, eeint16 or eeint8. For example:

eevar HourCounter

To declare a 4 byte array for emulating latching relays use eeint8

eeint8 RelayStore[4]

Only variables and strings can be stored in non-volatile memory, I/O ports and other objects

cannot.

When you read or write to a non-volatile variable, you are really reading and writing to a cache

memory. The underlying EEPROM is only written when something actually changes. This means

you can update your variables as often as you like with the same value. For instance to update

"RelayStore" with the status of Relay1 you could put the following in a loop.

if(Rly1) then RelayStore[0] = 1 else RelayStore[0] = 0 endif

The loop may be executed as fast as you wish, only a change in the state of RelayStore[0] will

get written to the EEPROM. As EEPROMs have a limited write endurance, this prevents

unnecessary wear.

A simple and eloquent method to update RelayStore is to give it its own thread.

eeint8 RelayStore[2]

thread RelayUpdate 50

RelayUpdate:

if(Rly1) then RelayStore[0] = 1 else RelayStore[0] = 0 endif

if(Rly2) then RelayStore[1] = 1 else RelayStore[1] = 0 endif

threadsuspend

main: if(RelayStore[0]) then Rly1 = 1 else Rly1 = 0 endif

if(RelayStore[1]) then Rly2 = 1 else Rly2 = 0 endif

threadstart RelayUpdate

... Do things ...

loop

In the start up section of main: there are a couple of lines of code to initialise the relays with

their stored settings. The RelayUpdate thread is then started which will keep the relays

updated every 50mS.

Take care when making variables non-volatile. EEPROMs have a limited write endurance of

about 1000000 (1 million) and if you change the values too frequently you can quickly reach

the end of their life. dScript can write a new EEPROM value every 320mS. If you do so you will